Printing apparatus and sheet cartridge

ABSTRACT

In a sheet feeding mechanism wherein a spring can be used to properly regulate a sheet feeding position, sheets are not deformed in spite of the urging force of the spring, and a required conveying force is prevented from being increased after sheet feeding. Specifically, immediately before a sheet is fed, a driving mechanism is used to move a slide plate leftward. A driving portion of the slide plate pushes an arm of a lever to rotate the lever counterclockwise against a tension spring. Thus, a connecting portion of the lever pushes an interlocking portion of a biasing plate downward. That part of the biasing plate rotates clockwise against the force exerted as a set spring portion is urged counterclockwise. In conjunction with this rotation, a biasing portion rotates clockwise to urge printing sheets to press them against a reference surface of a case.

This application is a divisional of U.S. patent application Ser. No.10/451,350, filed Jun. 16, 2003, and allowed Jul. 27, 2006.

This application claims priority from Japanese Patent Application No.2002-182159 filed Jun. 21, 2002, which is incorporated hereinto byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printing apparatus and a sheetcartridge, and more specifically to a mechanism that feeds printingsheets in a printing apparatus such as a printer or a copying machine.

2. Description of the Related Art

Conventional sheet feeding mechanisms of this type are provided with amechanism for properly maintaining a conveying position or posture of asheet during sheet feeding. The mechanism enables the sheet to beprevented from slant moving so that printing is executed to an accurateposition of the sheet during printing operation, which accompaniesconveying of the sheet after sheet feeding.

For example, in a known sheet feeding mechanism of a printer, a pair ofguide members is fixedly provided so that the distance between the guidemembers is slightly larger than the width of sheets. This arrangementserves to regulate the sheet feeding direction or position of thesheets. Further, in another known form, one of the guide members can bemoved depending on the size of sheets, while the sheets can be pressedagainst the other guide member. Furthermore, as described in, forexample, Japanese Patent No. 3180819, a copying machine provided with atamper is known wherein when sheets are stacked on a feeding section,the tamper biases the sheets in a direction crossing the sheet feedingdirection and presses the sheets as in the case with the above guidemembers.

However, the size of sheets such as their width may vary slightly. Inthis case, if the guide members are fixedly provided as in the aboveconventional example, looseness may be created between the guide membersand the sheets in accordance with the variation of the sheet width.Consequently, the sheets may be inclined in the conveying direction ofthe sheet.

Further, also in the form in which the guide member or the damper ispressed against a sheet, the guide member may be shifted because of theweight of sheets depending on the position of the printer because nourging force is basically exerted after the pressing. As a result, thesheets are inclined when fed. For example, if a sheet cartridge(cassette) is installed in a relatively small-sized portable printer,the load a few or several times the weight of sheets due to a vibrationor a shock caused by carrying of the printer may act on the guidemembers, depending on the position of the printer when it is carried.Thus, the guide members may be shifted to incline the sheet feedingdirection.

To solve this problem, it is considered that a spring may be used tourge and press the guide members against sheets. However, in aconfiguration in which this urging force always acts on the sheets, thesheets may be deformed, e.g. curled. Consequently, the relativepositions of the sheets and, for example, a print head may deviate fromthe original ones to reduce the accuracy of a print position. Further,if this urging force is allowed to act during printing, a relativelylarge force is required to convey fed sheets. This creates problems suchas an increase in the power consumption of a relevant motor and asdegradation of print quality due to an increase in a slip amount of theconveyed sheet.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a printing apparatusand a sheet cartridge which can use a spring to properly regulate asheet feeding position such as a sheet feeding direction and whichprevents sheets from being deformed in spite of the urging force of thespring, a conveying force required after sheet feeding from beingincreased, and a slip amount of the sheet conveyed from increasing.

In the first aspect of the present invention, there is provided aprinting apparatus including a sheet feeding mechanism and a conveyingmechanism for conveying a sheet fed by the sheet feeding mechanism andperforming printing on the sheet which is conveyed by the conveyingmechanism, the apparatus comprising:

urging means for urging the sheet fed in the sheet feeding mechanism ina direction different from a feeding direction of the sheet so as topress the sheet against a predetermined reference surface; and

control means for controlling the urging means so that the urging meansstarts the urging at least before the sheet feeding means exerts aconveying of the sheet for feeding.

In the second aspect of the present invention, there is provided aprinting apparatus using a sheet cartridge, in which sheet are housedand which is installed in the apparatus, the installing the sheetcartridge causing a sheet feeding mechanism to be formed, including aconveying mechanism for conveying the sheet fed by the sheet feedingmechanism, and performing printing on the sheet which is conveyed by theconveying mechanism, the apparatus comprising:

urging means, which is formed by installing the sheet cartridge, urgingthe sheet fed in the sheet feeding mechanism in a direction differentfrom a feeding direction of the sheet so as to press the sheet against apredetermined reference surface; and

control means for controlling the urging means so that the urging meansstarts urging at least before the sheet feeding mechanism performsconveying of the sheet for feeding.

Here, the control means may control the urging means so that the urgingmeans perform urging at least until the conveying mechanism startsconveying of the sheet.

In the third aspect of the present invention, there is provided aprinting apparatus using a sheet cartridge, in which sheet are housedand which is installed in the apparatus, the installing the sheetcartridge causing a sheet feeding mechanism to be formed, including aconveying mechanism for conveying the sheet fed by the sheet feedingmechanism, and performing printing on the sheet which is conveyed by theconveying mechanism, the apparatus comprising:

a first actuating member engaging with a first member of the sheetcartridge installed to form the sheet feeding mechanism; and

a second actuating member engaging with a second member of the sheetcartridge installed for forming urging means, which includes a springmember to urge the sheet to be fed by the sheet feeding mechanism in adirection different from a feeding direction of the sheet so as to pressthe sheet against a predetermined reference surface,

wherein the first and second actuating members are configured so thatthe urging means starts urging at least before the sheet feedingmechanism performs conveying of the sheet for feeding.

In the fourth aspect of the present invention, there is provided a sheetcartridge in which sheets are housed and which is used by a printingapparatus including a sheet feeding mechanism and a conveying mechanismfor conveying a sheet fed by the sheet feeding mechanism and performingprinting on the sheet which is conveyed by the conveying mechanism, thecartridge comprising:

a first member engaging with a first actuating member of the printingapparatus upon installation of the sheet cartridge to form the sheetfeeding mechanism, and a second member engaging with a second actuatingmember of the printing apparatus upon installation of the sheetcartridge to form urging means, which includes a spring member to urgethe sheet to be fed by the sheet feeding mechanism in a directiondifferent from a feeding direction of the sheet so as to press the sheetagainst a predetermined reference surface,

wherein the first and second members are configured so that the urgingmeans starts urging at least before the sheet feeding mechanism performsconveying of the sheet for feeding.

With this structure, the urging operation is performed to urge theprinting sheets fed in the sheet feeding mechanism in the directiondifferent from the sheet feeding direction to press them against thepredetermined reference surface. This urging operation is started atleast before one of the sheets is conveyed by the feeding mechanism soas to feed the sheet. Further, the urging operation is preferablyperformed at least until the conveying means starts conveying the sheet.Consequently, at least when the sheet is fed, its position such as itsfeeding direction can be regulated by exerting urging force on it.Furthermore, it is possible that the urging operation is performedimmediately before the sheet is fed and not on the other occasions,particularly while the sheet is housed before being fed. It is alsopossible that the urging operation is performed only during a sheetfeeding operation and not while the sheet is subsequently conveyed andprinted.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the main part of the configuration of anink jet printer according to an embodiment of the present invention asviewed from its side;

FIG. 2 is a view showing the details of a sheet feeding mechanism formedin the printer;

FIG. 3 is a view illustrating the details of a connection associatedwith the installation of a sheet cartridge in this printer and requiredfor the operation of a biasing plate;

FIG. 4 is a view illustrating the operation of the biasing plate;

FIG. 5 is also a view illustrating the operation of the biasing plate;

FIG. 6 is also a view illustrating the operation of the biasing plate;

FIG. 7 is a view showing the structure of the biasing plate; and

FIG. 8 is a view illustrating a joint used to supply ink in thisprinter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below in detailwith reference to the drawings.

FIG. 1 is a sectional view of the main part of the configuration of anink jet printer according to an embodiment of the present invention asviewed from its side.

The printer according to the present embodiment is relativelysmall-sized and portable one. It is composed of two parts including asheet cartridge and a printer main body the external shapes of which aregenerally defined by a sheet cartridge case 1 and a printer chassis 101,respectively. The sheet cartridge contains sheets 2 and an ink bag 7that stores ink used for printing by the printer main body. The sheetcartridge is detachably installed in the printer main body. Thus, thesheet cartridge can be replaced with a new one once a predeterminednumber of sheets housed have been used up or the ink inside the ink baghas been exhausted.

As shown in FIG. 1, the sheet cartridge case 1 comprises a chamber 1 ein which the printing sheets 2 are housed and a chamber 1 f in which theink bag 7 is housed. When the sheet cartridge case 1 is installed on theprinter chassis 101, it is possible to feed the sheets 2 housed in thechamber 1 e and to supply the ink in the ink bag 7 housed in the chamber1 f. Further, the installation of the sheet cartridge case 1 enables theoperation of a biasing plate 3 used to regulate the feeding direction ofthe sheets 2 or the like during sheet feeding, as described later indetail. A well-known arrangement can be used to install or remove thesheet cartridge in or from the printer main body. Its detaileddescription is omitted.

The printing sheets 2 housed in the chamber 1 e are separated from oneanother by a separating convex 1 a and a sheet feeding roller 112 (seeFIG. 2). Then the separated sheet is fed to a conveying mechanism of theprinter main body. The conveying mechanism provided in the printerchassis 101 is mainly composed of a pair of a conveying roller 102 and apinch roller 103 and a pair of a sheet discharging roller 104 and adischarging pinch roller 105 which are provided downstream of the pairof rollers 102, 103 in a conveying direction. A platen 106 is disposedalong the conveying path between these pairs of rollers to flatten aprint surface of the printing sheet 2 conveyed on the platen 106.

An area opposite the platen 106 corresponds to an area scanned by aprinting head 130. More specifically, the printing head 130 is installedon a carriage 107, and the carriage 107 is configured to be supported byshafts 108 and 109 and be reciprocated in a direction perpendicular tothe sheet of the drawing. Further, on the carriage 107 not only theprinting head 130 but also ink tanks 107 a, 107 b, and 107 c that storeink supplied to the print head 130 are installed. Thus, as the carriage107 is moved, the printing head 130 can be driven in accordance withprinting data to eject the ink onto the sheet 2. Then, by repeating thescanning of the printing head 130 and the conveyance of the sheet 2 by apredetermined amount, characters, images, or the like can be printed onthe entire sheet 2.

The tanks store cyan, magenta, and yellow inks, respectively. Theprinting head 130 comprises ejection opening arrays each composed of apredetermined number of ejection openings, correspondingly to thesethree types of ink. Each of the ejection openings is provided with aheater, which is an elctro-thermal converter, disposed in an ink path incommunication with the ejection opening. The ink is caused to generate abubble utilizing thermal energy generated by the heater when it isdriven. Then, the pressure of the bubble causes the ink to be ejected.Further, the carriage 107 can be moved by a carriage driving mechanismincluding a lead screw 110 provided parallel with the shafts 108 and 109and a driving mechanism such as a motor driving the lead screw. Further,a motor 127 provided under the platen 106 provides driving force servingto operate the biasing plate 3 as described later.

The printer chassis 101 is further provided with a joint mechanism 111.The joint mechanism 111 is formed of pipe materials to supply ink fromthe ink bag 7 in the sheet cartridge 1 to the ink tanks 107 a to 107 con the carriage 107. The joint mechanism 111 is held by a fixing section111 b and fixed to the printer chassis 1101.

As shown in FIG. 8 that is a sectional view of the sheet cartridge case1 as viewed from above, the joint mechanism 111 is composed of threeneedles 111A, 111B, and 111C corresponding to the cyan, magenta, andyellow inks. The fixing section 111 b holds these three needles 111A,111B, and 111C together and fixes them to the printer chassis 101.Specifically, the joint mechanism 111 has the joint needles 111A, 111B,and 111C corresponding to ink bags 7 a, 7 b, and 7 c, respectively.Thus, the ink bags 7 a, 7 b, and 7 c, storing cyan, magenta, and yellowinks, respectively, can be connected to the ink tanks 107 a to 107 c,respectively, for ink supply. Each needle of the joint mechanism 111 hasa pointed needle portion 111 a and a side hole for defining a liquidpath, which are formed at a tip of the needle. In conjunction with theinstallation of the sheet cartridge 1 in the printer main body, theneedles 111A, 111B, and 111C piece joint rubbers 9A, 9B, and 9C,respectively, sandwiched between a holder 8 and guide hole members 10A,10B, and 10C for the respective inks to accomplish the above connection,the holder 8 integrally constituting a joint portion for the ink bags.

Referring back to FIG. 1, the biasing plate 3 is formed of a platespring material. A flange portion 3 b of the biasing plate 3 isrotatably supported by a shaft 4 fixed to the sheet cartridge case 1.

FIG. 7 is a sectional view of the sheet cartridge case 1, showing thestructure of the biasing plate 3. As shown in this figure, in additionto the flange portion 3 b supported by the shaft 4 as described above,the biasing plate 3 includes a set spring portion 3 a, a biasing portion3 c, and an interlocking portion 3 d. As shown in FIG. 3, the set springportion 3 a abuts against the convex 1 c of the sheet cartridge case 1.Thus, the entire biasing plate 3 is always urged so as to rotatecounterclockwise with respect to the shaft 4. The biasing portion 3 c,formed opposite the set spring portion 3 a with respect to the rotatingshaft 4, moves clockwise as the interlocking portion 3 d is moved.Accordingly, the sheets 2 stacked in the chamber 1 e are urged in adirection generally orthogonal to the sheet feeding direction. Thesheets 2 can thus be biased. The interlocking portion 3 d moves inresponse to the movement of a lever 123 (FIG. 3) provided in the printermain body as described later in FIG. 3. Thus, the biasing portion 3 c,integrated with the interlocking portion 3 d, can perform an urgingoperation for the above biasing.

The biasing plate 3 is configured as described below. The set springportion 3 a and interlocking portion 3 d of the biasing plate 3 arearranged in the chamber 1 f of the sheet cartridge 1, in which the inkbags are housed, so that their movements will not interfere with theprinting sheets 2. The biasing portion 3 c is arranged in the chamber 1e, in which the printing sheets 2 are housed, so as to abut against theprinting sheets 2. Further, the width of the biasing portion 3 c (avertical length in FIG. 7) corresponds to the full height of the maximumnumber of sheets stacked together and is thus enough to urge thesesheets. In the present embodiment, only one biasing portion 3 c isprovided. However, a plurality of biasing portions 3 c may be providedalong the length direction (sheet feeding direction) of the stackedsheets. Furthermore, the biasing portion 3 c is formed integrally of aspring member. However, it should be appreciated that a resin materialmay be used in that part of the biasing plate which is contacted withthe sheet so as not to make a flaw such as a dent in the side of thesheet and so as to reduce loads imposed by biasing during sheet feeding.

Referring back to FIG. 1, reference numeral 6 denotes an opening andclosing door. When the sheet cartridge is removed from the printerchassis 101, the opening and closing door 6 is manually closed usingshafts 1 g and 1 h (see FIGS. 1 and 3) as an axis of rotation as shownin FIG. 7. This prevents dirt from adhering to the joint rubbers 9A, 9B,and 9C and also prevents the printing sheets 2 from slipping out of thecartridge case 1. On the other hand, when the cartridge is installed onthe printer chassis 101, in contrast with the operation of manuallyclosing the door, the door is opened by rotating, in FIG. 1, itclockwise through 90° to establish the condition shown in this figure.This makes it possible to join the ink to the ink tank and to feed theprinting sheets 2.

A mechanism (its essential parts are not shown in FIG. 1) for feedingthe sheets 2 is formed by installing the sheet cartridge on the printerchassis 101 as in the case with the joint for ink supply as describedabove.

FIG. 2 is a view showing the detail of the sheet feeding mechanismformed.

In this figure, reference numeral 112 denotes a sheet feeding rollerthat is supported so as to be rotatable using a shaft 114 of an arm 113.The sheet feeding roller 112 has a D-shaped cross section. Thus, as thesheet feeding roller 112 is rotated, the sheets are opposed by astraight D cut portion 112 a that is not involved in sheet feeding and acircular portion 112 b involved in sheet feeding. Reference numeral 115denotes a pressure plate. A projecting portion of the pressure plate 115is rotatively supported by a rotating shaft 116 fixed to the printerchassis 101. The pressure plate 115 can be pushed leftward by a pressingmember 120 to rotate clockwise around the rotating shaft 116, and apressing portion 115 a of the pressure plate 115 can press the sheetstoward the sheet feeding roller 112. The sheet feeding roller 112 isrotated in a condition that the pressure plate 115 presses the sheet 2against the circular portion 112 b of the sheet feeding roller 112, sothat the sheets 2 are moved toward the printer main body. Then, thesheets abut against the separating convex 1 a of the sheet cartridgecase 1, and the uppermost one of the stacked sheets 2 is separated fromthe others and then fed.

The sheet feeding roller 112 is driven by similarly transmitting thedriving force of a motor (not shown) via a gear train (not shown). Then,once a sheet feeding operation is finished, the sheet feeding roller 112stops at a rotary position where its D cut portion 112 a is parallelwith the sheet 2. Thus, when the sheet cartridge 1 is removed from theprinter chassis 101, the separating convex 1 a of the cartridge 1 isprevented from interfering with the sheet feeding roller 112 on thechassis 101 or vice versa. Further, when the sheet cartridge case isinstalled, the pressure plate 115 is controlled so as not be urged bythe pressing member 120. Thus, the pressing portion 115 a of thepressure plate 115 maintains its almost horizontal position, and as thecartridge case 1 is installed, the pressing portion 115 a enters a holeportion 1 b and can thus occupy a predetermined position in the sheetfeeding mechanism formed. Further, the pressing portion 115 a is set soas to operate within the range of the hole portion 1 a of the sheetcartridge 1 to avoid interfering with the sheet cartridge case 1 whenpressing the sheets 2 after the sheet cartridge case 1 has beeninstalled.

As in the case with the formation of the sheet feeding mechanism and ofthe joint for ink supply described above, a connection is establishedfor the operation of the biasing plate 3 as the sheet cartridge isinstalled.

FIG. 3 shows the details of the connection. In this figure, referencenumeral 117 denotes a slide plate having two slots 117 a and 117 bformed in a part of it. Positioning pins 118 and 119 fixed to theprinter chassis 101 engage with the slots 117 a and 117 b, respectively.Thus, the slide plate 117 can slide in the lateral directions of thefigure within the range of the slots. The slide plate 117 can be slid byusing a motor (not shown) to transmit its driving force through a cammechanism or the like. A well-known arrangement can be used for thispurpose, and its detailed description is omitted.

Further, a lever 123 engaging directly with the biasing plate 3 isprovided on that portion of the printer chassis 101 on which the sheetcartridge case 1 is installed. The lever 123 is generally L-shaped. Itsbent portion is rotatively supported by a rotating shaft 124 fixed tothe printer chassis 101. Consequently, the lever 123 as a whole can berotated. A tension spring 126 is attached to an end of an arm 123 a ofthe lever 123. The other end of the spring is fixed to the printerchassis 101. Consequently, the lever 123 is always urged clockwise. Onthe other hand, a stopper shaft 125 is fixed at a predetermined positionof rotation of the lever 123 resulting from the urging. Thus, theclockwise rotation of the lever 123 is limited to this position. Anotherarm of the lever 123 is a connecting portion 123 b. When the case of thesheet cartridge 1 is installed on the printer chassis 101, this armengages with the interlocking portion 3 d of the biasing plate 3 inconjunction with this installation of the cartridge.

The slide plate 117 comprises a driving portion 117 c that abuts againstthe arm 123 a of the lever 123, which serves to operate the biasingplate 3, and a holder portion 117 d that holds the pressing member 120,which drives the pressure plate 115. The pressing member 120 is fittedinto the holder portion 117 d of the slide plate 117 and is urgedleftward in the figure by a compression spring 122. In addition, alocking portion 121 is provided at the other end of the pressing member120 to prevent the pressing member 120 from slipping out of the holderportion 117 d. With this arrangement, as the slide plate 117 slidesleftward, the pressing member 120 abuts against the pressure plate 115.Thus, as described above in FIG. 2, the pressure plate 115 abuts thesheets 2 against the sheet feeding roller 112. In this abuttedcondition, when the slide plate 117 is moved further leftward, theholder portion 117 d of the slide plate 117 compresses the compressionspring 122. This compression load becomes a rotation torque to generatea pressing force that presses the sheets 2 against the sheet feedingroller 112.

Further, before the pressure plate 115 generates this pressing force,the driving portion 117 c of the slide plate 117 moves and abuts againstthe arm 123 a of the lever 123. Thus, before the pressure plate 115presses the sheets 2 against the sheet feeding roller, the sheets 2 canbe biased. Specifically, the leftward movement of the slide plate 117causes its driving portion 117 c to push the arm 123 a of the lever 123.As the slide plate 117 moves further leftward, the lever 123 is rotatedcounterclockwise against the tension spring 126, and the connectingportion 123 b pushes the interlocking portion 3 d of the biasing plate3, with which the interlocking portion 3 d is engaged, downward in thefigure. As a result, as shown in FIGS. 5 and 6, the biasing portion 3 cof the biasing plate 3 performs an operation of pressing the sheets 2downward in the figure, i.e. a biasing operation while the pressureplate is not exerting any pressing force.

Next, detailed description will be given mainly of a sheet feedingoperation involving a biasing operation performed in the printer of thepresent embodiment described above.

FIGS. 3 and 4 show a condition that the sheet cartridge case 1 isinstalled in the printer chassis 101. In FIGS. 3 and 4, the sheets 2 areshown being narrower at their right and left ends than in their centerin the figure and having round corners. Further, a similar shape is alsoshown in FIGS. 5 and 6. This is because after on the center of eachsheet 2 printing has been performed, both ends are cut off from thecenter, which has been printed, using perforations 2A. However, ofcourse, the application of the present invention is not affected by sucha sheet shape. It is apparent from the above description that thepresent invention is applicable to, for example, rectangular sheetsnormally used.

In the condition shown in FIGS. 3 and 4, the biasing portion 3 c of thebiasing plate 3 is not ready to bias the printing sheets 2. Accordingly,the position of the printing sheets 2 varies. For example, the sheets 2may be set against a reference surface 1 d formed by the case of thecartridge 1 as shown in FIG. 3 or may be separated from the referencesurface 1 d of the case 1 as shown in FIG. 4. In particular, the sheetfeeding roller often performs a sheet feeding operation on the sheetsinclined as shown in FIG. 4 and feeds them to a conveying section suchas the conveying roller 102 without eliminating the inclination. Ifthese sheets are printed, the print position is inclined relative to thesheets.

To prevent such a problem, the present embodiment biases the printingsheets 2 after the sheet cartridge 1 has been installed and immediatelybefore the sheet feeding roller 112 starts a sheet feeding operation.That is, it is important to perform this biasing operation beforepressing force acts on the sheets 2, the pressing force being exerted bythe pressure plate 115 to press the sheets 2 against the sheet feedingroller 112.

In FIG. 3, first, a driving mechanism such as the motor 127 is used tomove the slide plate 117 leftward in the figure. Accordingly, thedriving portion 117 c of the slide plate 117 pushes the arm 123 a of thelever 123 to rotate the lever 123 counterclockwise against the tensionspring 126 as shown in FIG. 5. Thus, the connecting portion 123 b of thelever 123 pushes the interlocking portion 3 d of the biasing plate 3downward in the figure. That part of the biasing plate 3 which ispresent to the right of the shaft 4 rotates clockwise against the forceexerted as the set spring portion 3 a is urged counterclockwise. Inconjunction with this rotation, the biasing portion 3 c rotatesclockwise. As a result, the biasing portion 3 c urges the printingsheets 2 to press them against the reference surface 1 d of the case 1.

In FIG. 5, in which the sheets 2 are pressed against the referencesurface, the pressing member 120 is abutted against the pressure plate115 as a result of the movement of the slide plate 117. However, thesheets 2 have not been pressed against the sheet feeding roller 112 yet.It is thus possible to bias the sheets 2 easily as shown in FIG. 5, evenwith the relatively weak pressing force of the biasing portion 3 c.

Then, in the condition shown in FIG. 5, when the slide lever 117 ismoved further leftward, the condition shown in FIG. 6 is established. Inthe condition shown in FIG. 6, the leftward movement of the slide plate117 rotates the lever 123 further counterclockwise to push theinterlocking portion 3 d of the biasing plate 3 further downward.However, since the length between the shaft 4 and the interlockingportion 3 d of the biasing plate 3 is set to be relatively large, theforce exerted by the biasing portion 3 c to press the sheets 2 is notsubstantially increased. In conjunction with the operation of thebiasing plate 3, the pressing member 120 moves leftward to rotate thepressure plate 115 to the condition shown in FIG. 2. In this case, theforce of the compression spring 122 of the holder portion 117 d alsoacts to rotate the pressure plate 115 to press the printing sheets 2against the sheet feeding roller 112. The pushing force of thecompression spring 122 is set so that the amount of rotation of thepressure plate 115 varies depending on the number of the printer sheets2 housed in the sheet cartridge. That is, with a large number ofprinting sheets 2, the amount of compression effected by the compressionspring 122 increases to press the printing sheets 2 with a strongerforce. On the other hand, with a smaller number of printing sheets 2,the amount of compression effected by the compression spring 122decreases to press the printing sheets 2 with a relatively weak force.Thus, a stable sheet feeding operation is possible even if the number ofthe printing sheets 2 changes.

Then, when rotating of the sheet feeding roller 112 feeds one of theprinting sheets 2 in the condition shown in FIGS. 6 and 2 and theconveying roller 102 and the pinch roller 103 (FIG. 1) are ready to feedthis printing sheet, i.e. when the sheet 2 is sandwiched between nipportions of the conveying roller 102 and the pinch roller 103, the motor127 is driven in a controlled manner so as to move the slide plate 117rightward. Thus, the slide plate 117 shifts from the condition shown inFIG. 6 back to the condition shown in FIG. 3. This stops the pressureplate 115 from pressing the printing sheets 2 upward and also stops thebiasing plate 3 from biasing the printing sheets.

As described above, the biasing operation of the biasing plate 3 startsimmediately before a sheet feeding operation is started and ends beforethe conveying force of the conveying roller in a conveying section actson the sheet. Consequently, at least when the sheet is fed, its positionsuch as its feeding direction can be regulated by exerting urging forceon it. Further, the urging operation is performed immediately before thesheet is fed and not on the other occasions, particularly while it ishoused before being fed. This prevents the deformation of the sheet orthe like caused by the urging force.

Further, the urging operation is performed only during a sheet feedingoperation and not while the sheet is subsequently conveyed and printed.Consequently, while the conveying roller and others are performing aconveying operation, the urging of the sheets by the biasing plate doesnot constitute resistance to the conveyance. This makes it possible todecrease conveying loads during printing.

Of course, a control section (not shown) drivingly controls the motor127, used to drive the slide plate 117. As is well known, the controlsection is composed of a CPU, a ROM, a RAM, and others.

It should also be appreciated that the application of the presentinvention is not limited to the above described portable printer. It isapparent from the above description that the present invention isapplicable to a printing apparatus such as a printer or a copier whichis used in a normal office or the like. Further, the sheet feedingsection need not necessarily be a cartridge. It may be a fixed sheetfeeding mechanism of the printing apparatus or a general auto sheetfeeder, which is removably used in the printing apparatus.

According to the above embodiment, the cartridge that can be installedin and removed from the printer has the presser spring used to bias theprinter sheets from the direction perpendicular to the conveyingdirection. The presser spring acts on the sheets immediately before asheet feeding operation is performed take one of the sheets out of thesheet cartridge. Consequently, the sheets are not curled in spite of theurging force of the biasing spring. It is thus possible to carry outaccurate printing without reducing printing accuracy.

Further, the presser spring, which biases the sheets from the directionperpendicular to the conveying direction, starts acting on the sheetsimmediately before a sheet feeding operation is performed take one ofthe sheets out of the sheet cartridge. The presser spring then ends thisaction immediately after the sheet feeding operation has been completed,when the conveying roller of the printer starts conveying the sheet.This hinders conveying resistance from being increased during printing,thus reducing the power consumption of the conveying motor and others.Further, the conveying resistance is prevented from being nonuinform,thus improving the printing accuracy. Furthermore, the urging force ofthe biasing spring also acts, only for a minimum time, on the sheetsstacked in the sheet cartridge in a print standby condition. This makesit possible to prevent the sheets in the print standby condition frombeing curled.

Furthermore, after the sheet cartridge has been removed from theprinter, the presser spring, which biases the sheets from the directionperpendicular to the conveying direction, does not act on the sheets.Consequently, even when the sheets are stored for a long time withoutbeing used or under hot and humid conditions, they can be prevented frombeing markedly curled or bent.

Further, ink the amount of which is sufficient to print the sheetsinstalled in the printer is housed in the cartridge that can beinstalled in and removed from the printer. In this case, the cartridgealso has the presser spring used to bias the printer sheets from thedirection perpendicular to the conveying direction. Further, the presserspring acts on the sheets immediately before a sheet feeding operationis performed take one of the sheets out of the sheet cartridge.Consequently, the sheets are not curled in spite of the urging force ofthe biasing spring. It is thus possible to carry out accurate printingwithout reducing printing accuracy.

As described above, according to the embodiment of the presentinvention, the urging operation is performed to urge the printing sheetsfed by the sheet feeding mechanism, in the direction different from thesheet feeding direction to press them against the predeterminedreference surface. This urging operation is started at least before oneof the sheets is conveyed so as to allow the sheet feeding mechanism tofeed it. Preferably, this operation is performed at least until theconveying means starts conveying the sheet. Consequently, at least whenthe sheet is fed, its position such as its feeding direction can beregulated by exerting urging force on it. Further, it is possible thatthe urging operation is performed immediately before the sheet is fedand not on the other occasions, particularly while it is housed beforebeing fed.

As a result, the spring or the like can be used to properly regulate thesheet feeding position such as the sheet feeding direction. Further, thesheets are not deformed in spite of the urging force of the spring orthe like. Furthermore, it is possible to prevent a required conveyingforce from being increased after sheet feeding.

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe intention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

1. A printing apparatus including a sheet feeding mechanism and aconveying mechanism for conveying a sheet fed by said sheet feedingmechanism and performing printing on the sheet which is conveyed by saidconveying mechanism, said apparatus comprising: urging means for urgingthe sheet fed in said sheet feeding mechanism in a direction differentfrom a feeding direction of the sheet so as to press said sheet againsta predetermined reference surface; and control means for controllingsaid urging means so that said urging means starts the urging at leastbefore said sheet feeding means exerts a conveying of the sheet forfeeding.